11,754 research outputs found
Cylindrically periodic dielectric waveguide at submillimeter waves
In the terahertz band, the availability of dielectric materials for fabrication of long waveguides is very limited. The only viable candidate at the current time appears to be fused quartz which unfortunately has a relatively low dielectric constant. This limits the use of standard Brag fibers which rely on higher dielectric constants. To overcome this limitation, we have examined the possibility of using a small number of low dielectric constant layers in a periodic arrangement and enclosing the entire structure with a metalic boundary. This configuration results in a moderate loss waveguide. Future work will include the manufacture and testing of such structures and a study of the bend losses
Physical optics characterization of a THz time domain system: UWB leaky lens antenna vs. Austin switch
In this work we show that a THz time domain system based on photoconductive antennas can be improved by over one order of magnitude by using the Ultra-wideband (UWB) leaky lens antenna. The system has been analyzed by implementing a physical optics method to characterize radiated fields by a silicon lens
Two-Stage Convolutional Neural Network for Breast Cancer Histology Image Classification
This paper explores the problem of breast tissue classification of microscopy
images. Based on the predominant cancer type the goal is to classify images
into four categories of normal, benign, in situ carcinoma, and invasive
carcinoma. Given a suitable training dataset, we utilize deep learning
techniques to address the classification problem. Due to the large size of each
image in the training dataset, we propose a patch-based technique which
consists of two consecutive convolutional neural networks. The first
"patch-wise" network acts as an auto-encoder that extracts the most salient
features of image patches while the second "image-wise" network performs
classification of the whole image. The first network is pre-trained and aimed
at extracting local information while the second network obtains global
information of an input image. We trained the networks using the ICIAR 2018
grand challenge on BreAst Cancer Histology (BACH) dataset. The proposed method
yields 95 % accuracy on the validation set compared to previously reported 77 %
accuracy rates in the literature. Our code is publicly available at
https://github.com/ImagingLab/ICIAR2018Comment: 10 pages, 5 figures, ICIAR 2018 conferenc
UWB leaky lens antenna as an improved performance emitter in a THz time domain system
In this contribution we introduce the use of the UWB leaky lens antenna as an improved photo-conducting emitter for a THz time domain system. The UWB antenna presents nearly constant impedance and directive symmetric patterns over a decade of frequency bandwidth. Currently, we are working towards the fabrication of a demonstrating prototype
Snyder noncommutative space-time from two-time physics
We show that the two-time physics model leads to a mechanical system with
Dirac brackets consistent with the Snyder noncommutative space. An Euclidean
version of this space is also obtained and it is shown that both spaces have a
dual system describing a particle in a curved space-time.Comment: 5 pages, RevTeX4. References adde
Exploiting optical near fields for phase change memories
We apply a recently developed technique based on optical near fields to achieve reversible phase switching in Ge2 Sb2 Te 5 films. By placing dielectric microspheres at the film surface and exposing them to pulsed laser light, a complex intensity distribution due to the optical near field can be created at the film surface. We demonstrate writing and erasing operations of patterns through phase switching. Spheres can be removed after an operation by optical near fields without ablation. Data erasure is achieved with and without near fields. The erasure method used can be determined from the result and erased information can be retrieved although being inverted. Three distinct material states are identified within patterns, showing clear contrast and sharp borders between them, thus opening the possibility of three-level data storage. Our results suggest that optical near fields are a promising candidate for developing strategies in data storage, encryption, and multiplexing. © 2011 American Institute of Physics.Peer Reviewe
An Introduction to the Covariant Quantization of Superstrings
We give an introduction to a new approach to the covariant quantization of
superstrings. After a brief review of the classical Green--Schwarz superstring
and Berkovits' approach to its quantization based on pure spinors, we discuss
our covariant formulation without pure spinor constraints. We discuss the
relation between the concept of grading, which we introduced to define vertex
operators, and homological perturbation theory, and we compare our work with
recent work by others. In the appendices, we include some background material
for the Green-Schwarz and Berkovits formulations, in order that this
presentation be self contained.Comment: LaTex, 23 pp. Contribution to the Proceedings of the Workshop in
String Theory, Leuven 2002, some references added and a comment on ref. [16
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